With multi-stage vehicle automatic transmissions and automatic vehicle manual transmissions known from conventional use, hydraulic shifting elements designed as clutches or brakes are used for inserting different transmission stages of the transmission. In this process, for changing or inserting a desired transmission stage of the transmission, the hydraulic shifting elements are pressurized or vented with fluid pressure (fluid pressure is relieved). Fluid valves, in particular pressure control valves, are used for this purpose.
The current standard fluid valves for vehicle transmissions, for example, that which is disclosed in WO 2005/026858 A1, has two poppet valves interconnected at a hydraulic half-bridge circuit. Such a fluid valve has an inlet opening and two outlet openings, whereas, in terms of flow engineering, a first part valve is arranged between the inlet opening and the first outlet opening, and a second part valve is arranged between the first outlet opening and the second outlet opening. Thereby, the part valves are mechanically coupled in such a manner that the part valves alternately close or open. A single electromagnetic actuator is used for the actuation of the part valves.
Equipping such a fluid valve with a flow control device is known from WO 2009/092488 A1. The valve is provided with several channel areas, such that the fluid flowing in the direction of the second part valve is brought into a swirl. Thereby, the second part valve is designed as a cone poppet valve. Here as well, a single electromagnetic actuator is used for the actuation of the part valves.
The fluid valves known from these two documents are so-called “proportional pressure control valves.” In operation, such valves are set to a desired fluid pressure p at one of the outlet openings (to the working pressure connection), whereas such fluid pressure is essentially dependent in a proportional manner on an electric current I, which is supplied to the electromagnetic actuator. Thus, on the basis of the supplied electric current I, the desired fluid pressure p may be directly preset. As such, a p/I characteristic curve of such a proportional pressure control valve is essentially line-shaped in the normal operating range; i.e., the output fluid pressure p there is proportional to the supplied electric current I.
However, in some situations, such a purely proportional manner of operation is not advantageous. This is especially the case when, on the one hand, a fluid valve is to be set at low fluid pressures with a very high accuracy, and on the other hand high fluid pressures are to be made available. For precision control of a low fluid pressure, fluid valves require a very flat p/I characteristic curve, as current fluctuations thereby only slightly affect the output fluid pressure. In order to then set a proportional pressure control valve at a high fluid pressure, given the flat p/I characteristic curve, a very large electric current is necessary, which is possibly not available.
Fluid valves with a progressive p/I characteristic curve are known. Their p/I characteristic curve is relatively flat at low fluid pressures/currents (relatively low inclination) and relatively steep at increased fluid pressures/currents (relatively high inclination). Therefore, the p/I characteristic curve for such valves is not line-shaped, or is only partially line-shaped. Thereby, both a more precise setting of low fluid pressures, and a provision of higher fluid pressures, is possible.
A fluid valve with a progressive characteristic curve can be taken from, for example, DE 102 55 414 A1. For the production of the progressive characteristic curve, the electromagnetic actuator provided there, which serves the purpose of actuating the valve, has a two-part solenoid armature, whereas the armature parts are pushed away from each other by means of a spring. A complex assembly of the electromagnetic actuator, and thus the fluid valve, arises from the many individual parts of the solenoid armature,
An electromagnetic actuator is also known from DE 199 53 788 A1; with this, a disproportionately large force is achieved in an end position of the armature, by providing two pole faces on one magnetic yoke of the actuator, with each pole face interacting in succession with a tapering (cone-shaped surface of the armature) for the generation of the actuating force of the actuator. Thereby, the first of the pole faces is provided in an interior space radially enclosed by a solenoid coil of the actuator, and the second of the pole faces is provided outside of this interior space.
The travel path of such electromagnetic actuator is restricted by the second pole face, since it is located in the armature's direction of movement. In addition, a significant interaction between the second pole face and the armature can be achieved at a point that is very late, almost at the end of the travel path of the actuator, since only at that point have the armature and the second pole face sufficiently converged (the air gap between them is then sufficiently reduced). The actuating force path characteristic curve of the actuator correspondingly increases in a progressive manner for the first time at the end of the maximum possible travel path (see FIG. 3 of DE 199 53 788 A1: the actuation here takes place from right to left; i.e., the armature moves in the direction of actuation from s>0 to s=0).